Enzyme replacement therapy has been shown to be extraordinarily effective for patients with Type 1 (non-neuronopathic) Gaucher's disease. We now need to develop procedures to deliver useful amounts of enzymes to the brain in patients with hereditary metabolic storage disorders. We shall examine the effect of human placental beta-galactosidase on the amount of ganglioside GM1 in animal analogues of human generalized (GM1) gangliosidosis using a new intracerebral protein delivery system.